MarchieB: I would also not be surprised if you could advance past Legend using solely H2H
You can go all the way to TC that way. It's been done. i think Tita hit TC with hardly any if any RRs played.
I went from TL to C with 69 RRs played from the time I hit TL. and i had a 60.02 avg at the time.
What their algorithms are who knows. but it's definitely possible to Tier without RRs being much if any of a factor.